Debt (Summary Of Interest Expense) (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Disclosure Debt Summary Of Interest Expense [Abstract]
Cash payments for interest	$ 73	$ 109	$ 138	$ 215
Non-cash interest	1	3	5	7
Net changes in accruals	(35)	(59)	(25)	(60)
Total interest expense	$ 39	$ 53	$ 118	$ 162